I made & installed primer tube for 2.7cu Husky Challenger gas engine in my Aerotech P-51D Blondie for the same reason. I use a small eye dropper to deliver fuel thru the primer tube to the carburetor inlet. There are pictures of this set-up on my website, scroll down to 2.7 gas engine to see the primer tube, etc.. Here's a direct link to the fuselage section: http://waltsrchanger.com/html/fuselage1.html

Hope this will help you solve your problem.

Walt Carnes
www.waltsrchanger.com